1. Field of the Invention
The present invention relates to cerium (Ce) doped phosphor materials for solid-state lighting applications.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
White light-emitting diodes (LEDs) have been considered as next generation light sources as well as components in display devices because of their high efficiency, reliability, and long operating lifetime. In order to make white LEDs, there are basically two methods; one is to mix different red, green, and blue components from LED chips, and the second is to down-convert the emission from a blue LED or ultraviolet (UV) LED to a longer wavelength using a phosphor (e.g. the combination of blue-emission from a blue LED with a yellow-emission from phosphor materials under excitation by the blue light source).
In terms of cost, efficiency, simple fabrication, and high brightness, the second method (coating a yellow-emitting phosphor on a blue LED) has been widely used for fabrication of white LEDs (disclosed in PCT Patent Publication No. WO 98/05078 [9]). In display device applications, for example, such as a backlight unit for a liquid crystal display (LCD), it is also important to obtain a suitable color temperature using the yellow-emitting phosphor.
Y3Al5O12:Ce3+ (YAG:Ce3+) is one of the few phosphor materials for long blue or UV wavelength excitation sources. However, because YAG:Ce3+ phosphor has a relatively weak light emitting intensity in the red spectral region, it is difficult to obtain a good color rendering index (CRI, Ra).
Consequently, many groups have studied intensively in the field of yellow-emitting phosphors. For example, Park et al. [1] and Xie et al. [2] reported on Sr2SiO4:Eu2+ and Ca-α-SiAlON:Eu2+ phosphors, respectively.
Until now, however, no competing yellow phosphor has been found replace to the YAG:Ce3+ phosphor. Nonetheless, there is a need for new yellow phosphors that provide improved efficiency and color rendering properties in the red spectral region. The present invention solves this need and discloses anew yellow-emitting phosphor for solid-state lighting and display applications.